It depends. A well-managed transition wouldn't necessarily change much.
There isn't anything particularly remarkable about the current value. Yes the price has gone up recently and some might attribute that to this announced Tron deal but I'm not so sure. Steem's market cap ranking is about where it was for most of the past year when frankly nothing visible was going on. It seems to be mostly going with the flow of a mild 'alt season'. Actual development supported by SPS would be an improvement.
But of course, we'll have to wait and see how it plays out.
While you're clearly right about all else herein, it's just unreasonable to fail to anticipate a price decrease with a fork under such conditions IMHO. It's not like history hasn't provided examples.
If 'Steem Classic', or Gold, or Cash, or whatever name the new chain settles on, rises in price rather than declines, it would be the first fork to do so.
None of the other blockchain 'fork' examples you allude to are really analogous. Most of them (e.g. Bitcoin gold) are third party forks created by opportunists. Ethereum Classic is very much a special case and also very different as it didn't involve the founder selling out to a competing chain/foundation, but instead actively supporting the non-Classic chain.
Anyway, after the live streem, the lastest is that the token swap is off for now and the existing Steem blockchain will continue as before. I would imagine most fork proposals will accordingly off the table, but who can say going forward. I expect many in the Steem community to remain skeptical of the new corporate overlords (which a blockchain doesn't really have), as well they should.